The invention concerns a highly reliable hydraulic actuator designed in particular but not exclusively for operating mechanical parts of aircraft such as control surfaces, ailerons or deflectors within a flight control system or even aircraft front wheel steering systems.
In known flight control systems, reliability requirements applying to civil aircraft in particular make it necessary to provide multiple (in practice three) hydraulic circuits to hydraulic actuators with at least one able to take over from another should the latter fail. This redundancy is reflected in a significant increase in weight and overall size; in practice, there is the additional requirement to achieve high reliability for each circuit.
An object of the invention is to alleviate the aforementioned drawbacks by making it possible to reduce the number of hydraulic circuits needed, without reducing the level of reliability, by combining with at least one electro-hydraulic servocontrol unit a local pump system specific to that servocontrol unit or adapted to cooperate with multiple adjacent servocontrol units, designed to operate only in an emergency and operating on a limited volume of fluid, preferably contained for the most part in the servocontrol unit in question, sourced from the main hydraulic circuit, possibly through valves.
More generally, the invention is directed to being able to operate on a double-acting actuator system (either a double-acting actuator or opposed single-acting actuators), of the linear of rotary type, at will, hydraulically or hydrostatically, the hydraulic mode being preferably, but not necessarily, a normal mode.
The invention, therefore, proposes an hydraulic actuator composed of at least one double-acting actuator system, a mobile switching member disposed in a housing connected hydraulically to the actuator system and via an hydraulic distribution unit to fluid inlet and outlet pipes incorporating isolating valves, a fluid reserve connected to the outlet pipe, and a control member adapted to command the mobile switching member to move between a neutral configuration in which the actuator system is isolated hydraulically from the hydraulic distribution unit and an active service configuration in which the actuator system communicates with the hydraulic distribution unit, characterized in that it further includes a variable speed controlled pump system connected by an auxiliary branch circuit to the housing of the mobile switching member and to the fluid reserve, the mobile switching member having three positions and being provided with additional control means adapted to command the mobile switching member to move between the neutral configuration and an active second configuration in which the actuator system communicates with the auxiliary circuit, whereby the actuator system, the pump system and the auxiliary circuit constitute a hydrostatic transmission.
It will be understood that a pump system of this kind (which may have a backup function), provided that appropriate hydraulic connections are provided (which is within the competence of one skilled in the art), may control multiple systems of actuators through associated mobile switching members, the control of each actuator system being individualized by selectively acting on the associated mobile member.